Adsorption of H2O, NH3 and C6H6 on alkali metal cations in internal surface of mordenite and in external surface of smectite: a DFT study
Adsorption of H2O, NH3 and C6H6 on alkali metal cations in internal surface of mordenite and in external surface of smectite: a DFT study
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DOI：
10.1007/s00269-008-0276-9
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发表时间：
2009-05
影响因子：
1.4
通讯作者：
L. Benco;D. Tunega
中科院分区：
文献类型：
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作者：
L. Benco;D. Tunega
采用密度泛函从头计算方法研究了H2O、NH3和C6 H6在丝光沸石的H-和碱金属交换结构以及蒙脱石层上相应阳离子的吸附.质子或碱金属阳离子补偿一个Al/Si骨架取代，并驻留在沸石的骨架外位置或靠近Al/Si取代的平坦蒙脱石层上方。沸石和蒙皂石在吸附能和阳离子位置随阳离子性质变化的规律上具有明显的相似性。计算得到的吸附能呈现以下趋势：E（NH3）>E（H2O）>E（C6 H6）。由于与骨架的接触较松，沸石阳离子是较强的吸附中心，计算的沸石吸附能比蒙脱石阳离子大约20-30%。最高的吸附能计算为H-交换的结构和碱金属阳离子的组的吸附能的降低被观察到。吸附能偏离平稳变化的原因是：（1）H交换结构中强氢键的形成，（2）吸附诱导的外部Li+阳离子迁移，（3）吸附在笼形分子阳离子上的扁平C6 H6分子的空间位阻。
Adsorption of H2O, NH3and C6H6on H- and alkali metal-exchanged structures of mordenite and on corresponding cations on the smectite layer is investigated by ab initio density-functional calculations. Proton or an alkali metal cation compensates one Al/Si framework substitution and resides in the extra-framework position of zeolite or above flat smectite layer close to the Al/Si substitution. Pronounced similarities between zeolite and smectite are observed in changes of the adsorption energies and location of the external cation with changing character of the external cation. Calculated adsorption energies exhibit the following trend:E(NH3) >E(H2O) >E(C6H6). Because of looser contact with the framework, zeolitic cations are stronger adsorption centers and calculated adsorption energies of zeolites are by ~20–30% larger than cations of smectites. The highest adsorption energy is calculated for H-exchanged structures and down the group of alkali metal cations a decrease of the adsorption energy is observed. Deviations from the smooth variation of the adsorption energy are caused by: (1) formation of strong hydrogen bonds in H-exchanged structures, (2) adsorption induced migration of the external Li+cation, and (3) steric hindrances of the flat C6H6molecule adsorbed on the cation in the cage of zeolite.